The present invention relates to a variable venturi-type carburetor.
In an engine, it is preferable that a lean air-fuel ratio be used when the engine is operating under an idling state in order to promote a lower specific fuel consumption; that another lean air-fuel mixture, which is far leaner than the lean air-fuel mixture used at the time of idling, be used in the normal cruising operation of a vehicle in which cruising operation a stable combustion can be obtained as compared with the combustion obtained at the time of idling; and that a rich air-fuel mixture be used at the time of acceleration in order to obtain good acceleration. Consequently, it is necessary to change the air-fuel ratio so that at least three separate air-fuel ratios are obtained in accordance with the operation condition of the engine. In a conventional fixed venturi-type carburetor, in order to obtain such separate three air-fuel ratios, control of the air bleed of the slow fuel system, control of the air bleed of the main fuel system and the control for increasing the amount of fuel fed from the main fuel system are carried out. Consequently, in a conventional carburetor, the control system of air-fuel ratio becomes complicated. Thus, problems occur in that the reliability of the control system will deteriorate, and that the manufacturing cost of the control system will be increased.